To design safe buildings, fire safety engineers must understand how occupants behave during a fire emergency. In simple terms, the time occupants take to evacuate to a place of safety must not exceed the time it takes for fire conditions to become untenable within the building or along the evacuation path.

Required Safe Egress Time

In fire engineering, this assessment is known as a RSET/ASET analysis. The fundamental principle is that the Required Safe Egress Time (RSET) must be less than or equal to the Available Safe Egress Time (ASET). If the required time is longer than the available time, conditions will become life-threatening before occupants can safely evacuate.

An equation has been formulated to calculate RSET. It is measured from the time a fire ignites until the time that all occupants have evacuated to a safe location. It is made up of several components: the cue period, response period, delay period, and movement period.

The cue period is the time taken for occupants to become aware that a fire has occurred. This may be through a fire alarm, the sight or smell of smoke, or verbal warnings such as someone shouting “fire”. The response period follows, during which occupants decide what action to take.

Studies on human behaviour shows that occupants do not always evacuate immediately after becoming aware of a fire. Some will gather personal belongings, some will contact friends or family, some will attempt to fight the fire. This is called the delay period.

The final component, the movement period, is when occupants physically travel along evacuation routes and exit the building to a place of safety.

Incorrect actions people take during this time can result in injury and death. Unfortunately, we have seen this happen time and time again.

Examples of Human Behaviour during a Fire

Lacrosse apartment, Melbourne, Victoria

On 25 November 2014, a fire started on the balcony of Apartment 805 of the 23-storey Lacrosse apartment at 673–675 La Trobe Street, Melbourne. Although the building was equipped with three portable fire extinguishers on each residential floor, none were used by occupants. The fire spread rapidly along the external façade, reaching the top of the building in minutes.

Firefighters successfully extinguished the fire and all residents evacuated safely; however, the incident resulted in approximately $12 million in damage. Post-fire investigations revealed that the apartment smoke detector had been covered with aluminium foil, preventing it from activating. It was also found that the occupant initially attempted to extinguish the fire using a container of water, which was ineffective.

Apartment in Ottawa, Canada

On 31 January 1997, a fire broke out in the closet at the entrance door of a 6th floor apartment in Ottawa, Canada, where an elderly couple lived. The building was provided with many fire safety measures such as fire hose reels, fire phones, self-closing tubular-core 45mm thick timer doors at every apartment and egress stair, and more.

Upon noticing the fire, the male occupant chose not to evacuate with his wife. Instead, he ran to the bedroom to call the fire brigade. Smoke had already entered the bedroom, prompting him to open the balcony door in an attempt to ventilate the space. This action instead introduced additional oxygen, intensifying the fire. Tragically, he was then unable to reach his wife, who later died from her injuries.

Apartment in Bankstown, New South Wales

On 6 September 2012, a fire broke out on the balcony of Unit 53 at 4 West Terrace, Bankstown, New South Wales. The building was provided with fire doors, portable fire extinguishers, internal fire hydrants and automatic fire detection and alarm systems.

After becoming aware of the fire, a male tenant opened the balcony door and attempted to extinguish the fire using a container of water. However, the flames increased, producing dense black smoke that entered the apartment.

The male tenant then exited the unit, leaving the balcony door open and propping the apartment entrance door open with a dumbbell. These actions increased the fire’s intensity and smoke spread. Two female occupants remained inside, sheltering in a bedroom and becoming trapped. As temperatures rose, they were forced to jump from a window. One woman died and the other sustained serious injuries.